Metal thin film resistors are well known and may be formed using a variety of resistive metals. Nichrome (NiCr) and sichrome (CrSi) are two that are commonly used. These types of thin-film resistors are formed in the back end (BEOL) of an integrated circuit manufacturing flow. BEOL resistors have less parasitic capacitance than resistors (typically polysilicon, silicide, or nwell) formed in the front end of line (FEOL) since they are formed at a greater distance from the substrate. BEOL resistors are preferred for high frequency RF applications because of the lower capacitance.
Integrating a metal thin film resistor in the BEOL of an integrated circuit manufacturing flow adds cost and cycle time. A typical metal thin film resistor is illustrated in FIG. 1. The metal thin film resistor 112 is formed on a third dielectric layer 110. The third dielectric layer is formed on an etch stop layer 108 which overlies lower interconnect leads 104. The lower interconnect leads 104 are embedded in a second dielectric layer 106. The lower interconnect leads 104 may be a first level of interconnect connected to diodes in an underlying integrated circuit 100 through a contact 101 or may be connected to an underlying level of interconnect through a via 101.
The area of the metal thin film resistor 112 is defined by a first resistor photoresist pattern. A second resistor photoresist pattern is used to define via landing pads 114 that form electrical contact to each end of the metal thin film resistor 112. The via landing pads 114 protect the thin metal thin film resistor from damage during etching of the resistor vias 120 and 122 which may result in high via resistance. A third resistor photoresist pattern is used to form openings for vias, 120 and 122, to make electrical connection to the via landing pads 114.
The cost of 3 additional lithography steps plus additional process steps to form the via landing pads 114 and to form resistor vias, 120 and 122 adds considerable expense and cycle time to the manufacturing flow.